That gathering will decide the party's referendum position - whether to remain within the EU, or line up with the DUP and recommend leaving.

But the UUP is demanding greater clarity around a number of "uncertainties" voters will have to weigh up.

Mr Nesbitt argued that while there were four months before the June 23 poll, questions on how an exit might affect Northern Ireland were "different and more urgent".

He said he pressed the point with Mr Cameron at a meeting in Downing Street yesterday, and the PM accepted the argument.

The UUP delegation also put five questions to Mr Cameron and said they expected him to answer them during his visit.

"First is the money, not just for farmers but also the voluntary and community sector, industry and our seats of learning," Mr Nesbitt said.

"Second, can we assume that outside the EU there would be no hit on the block grant from lowering the rate of corporation tax? The Prime Minister promised to reflect on that proposition.

"Third is the question of our land border in the event of a Brexit. This is a matter he is giving urgent consideration, but he also makes the point that the Brexit supporters also need to offer clarity on that point. "Fourth is welfare, immigration and asylum seekers.

"And finally, but as importantly, there is the sovereignty question, particularly the existential threat to the United Kingdom should there be an overall vote for Brexit, but with Scotland voting to remain.

"The Prime Minister has promised to answer these questions on his forthcoming visit which will precede the meeting of the Ulster Unionist Party's ruling executive, which will meet to consider the party's position on Saturday, March 5, 16 weeks before the referendum."

Previously Mr Nesbitt had said: "All things being equal, I would hope to recommend that we stay in."

While, at the time, his party wanted to see the outcome of Mr Cameron's negotiations with the UK's European Union partners on a range of issues, Mr Nesbitt had argued a vote to leave the union could pose an "existential threat" to the UK's future

In the event a majority of voters in Scotland are in favour of remaining, while England and Wales votes to exit, another Scottish independence referendum could be triggered.

"As I see it, as a unionist, Brexit is about uncertainty," Mr Nesbitt said at an event organised by the Centre for Cross-Border Studies several months ago.